Engines may use cam switching systems to adjust valve lift and valve opening duration of cylinder poppet valves. By adjusting valve lift and valve opening duration, it may be possible to tailor valve operation for engine operating conditions so that engine performance and efficiency may be improved. For example, reduced valve lift and shorter valve opening time durations may be applied at lower engine speeds and loads. On the other hand, higher valve lift and longer valve opening durations may be applied at higher engine speeds and loads. Additionally, cam switching systems may be used to deactivate selected engine cylinders during low driver demand conditions to increase efficiency of operating engine cylinders.
U.S. Pat. No. 7,404,383 describes an example cam switching system where an engine includes a camshaft with multiple outer sleeves that include lobes and the sleeves are splined to a central camshaft. By engaging a pin into a grooved hub in each sleeve, the axial position of the sleeve can be adjusted so that a different cam lobe engages a roller finger follower (RFF) that operates a poppet valve. However, it may be possible to command the pin into the groove without the pin actually entering the groove and without the cam profile switching. For example, if the pin does not extend when a solenoid is supplied electrical current, the cam profile may not switch from a first profile to a second profile. Consequently, if the engine control system adjusts the fuel amount in response to the expected activated cam profile, engine torque and air-fuel ratio may degrade.
The inventors herein have recognized potential issues with operating a cam profile switching mechanism and have developed a method for determining engine state, comprising: commanding a cam sleeve to move axially; providing a signal indicative of a presence or an absence of the cam sleeve moving axially, the signal provided responsive to rotation of a feature of the cam sleeve; and adjusting an engine actuator responsive to the signal.
By determining axial movement of a cam sleeve via rotation of a feature of the cam sleeve, it may be possible to determine which of a plurality of cam profiles is presently active. For example, a rotation sensing cam profile sensor may be located at a fixed position where it may detect rotation of one or more cam sleeve features that are indicative of cam sleeve axial position. A first rotating feature of the cam sleeve may indicate that a first cam profile is presently active while a second rotating feature of the cam sleeve may indicate when a second cam profile is active. In this way, an activated cam profile may be determined so that an engine torque actuators may be adjusted in a desirable manner.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.